<template>
    <ul class="list">
        <li class="item" 
        v-for="(item, key) of letters" 
        :key="key"
        @touchstart.prevent="handleTouchStart"
        @touchmove="handleTouchMove"
        @touchend="handleTouchEnd"
        @click="handleLetterClick"
        :ref="item"
        >{{item}}</li>
    </ul>
</template>

<script>
    export default {
        name: 'CityAlphabet',
        props: {
            cities: Object
        },
        data() {
            return {
                touchStatus: false,
                startY: 0,
                timer: null
            }
        },
        updated(){
            this.startY = this.$refs['A'][0].offsetTop
        },
        computed: {
            letters(){
                const letters = []
                for(let i in this.cities){
                    letters.push(i)
                }
                return letters
            }
        },
        methods: {
            handleLetterClick(e){
                this.$emit('change', e.target.innerText)
                window.console.log(e.target.innerText)
            },
            handleTouchStart(){
                this.touchStatus = true
            },
            handleTouchMove(e){
                if(this.touchStatus){

                    // 截流操作
                    if(this.timer){
                        clearTimeout(this.timer)
                    }
                    this.timer = setTimeout(()=>{
                        const touchY = e.touches[0].clientY - 79
                        const index = Math.floor((touchY - this.startY)/22)
                        if(index >=0 && index < this.letters.length){
                            this.$emit('change', this.letters[index]) 
                        }
                    }, 16)
                }
            },
            handleTouchEnd(){
                this.touchStatus = false
            }
        }
    }
</script>

<style scoped lang='stylus'>
@import '../../../assets/styles/varibles.styl'
    .list
        position absolute
        right 0
        top 1.58rem
        bottom 0
        width .4rem
        display flex
        flex-direction column
        justify-content center
        align-items center
        .item
            height .44rem
            line-height .44rem
            color $bgColor


</style>